Multiple fracturing of oil, gas and coal bed methane-bearing formations, where such formations have low permeability (i.e. “tight” reservoirs) are typically necessary to adequately produce hydrocarbons. Various of such methods are now fully commercialized in the prior art as primary oil and/or gas recovery methods.
Two types of completions for fracturing formations that are currently employed are Packers Plus Energy Services Inc.'s StackFrac™1 process which uses open hole completions, and lined/cemented completions using technology (valves, liners, and the like) supplied by Halliburton Company. A horizontal hole is drilled low in the target consolidated tight-rock hydrocarbon reservoir. In the Halliburton technology, a liner is emplaced in the hole and cemented-in. This assures that there is no direct communication between the future induced fractures along the outside of the wellbore. In the Packers Plus technology, the fractures are accomplished from an open hole-there is no liner. Isolating packer seals (“packers”) situated on injection tubing are actuated down-hole when in the well, so as to press against the rock itself in order to isolate the zones when conducting fracturing operations and create fissures in the rock, which typically extend upwardly from a horizontal wellbore. After the fracturing operation, the packers are deactivated and all fractures then produce to the surface, in a process termed “primary production” which terminology is adopted and used herein. Fractures are kept open by the deposit within the fractures of a “proppant” that has been carried into the fractures by the fracturing fluid. Proppants typically consist of sand, metallic or ceramic balls, and/or various chemicals, and provide a relatively high permeability flow channel. Formation fluids that flow into the fractures then easily drain to production tubing within the horizontal hole or wellbore for conveyance to the surface. 1StacFrac™ is a registered trademark of Packers Plus Energy Services Inc. for inter alia the wares of packers, frac-ports, and ball seats.
A major characteristic and benefit of multiple-induced fractured reservoirs is high initial production rates. Problematically, however, when producing from all fractures simultaneously the production rates for such reservoirs typically suffer rapid decline as pressure drops within the formation, for reasons as explained below. The multiple fracturing process is expensive, and the overall recovery factors for these types of formations are typically low, usually achieving recovery factors of less than 10% for oil. In order to maintain satisfactory field-wide production rates, a vigorous program of capital-intensive drilling of new multiple-fractured wells is required to compensate for the high decline rate. The oil production mechanism is by solution gas drive, and thus there is a rapid decline in the reservoir pressure which is detrimental to the potential future oil recovery. In this regard, as solution gas comes out of solution with declining pressure within the formation, the viscosity of the remaining oil increases because light components are removed from the oil.
Furthermore, two-phases of intermingled oil and gas are established, thereby decreasing the oil relative permeability and further reducing production rates. Consequently the oil flow rate decreases rapidly.
Because hydrocarbons such as shale gas and coal bed methane occur in formations of low permeability, recovery of these types of hydrocarbons particularly suffer from low recovery factors.
What is needed is a hydrocarbon recovery method for use in conjunction with multiple-fractured tight reservoirs, so as to reduce or limit the rapid decline in pressure in the formation which typically results, and to limit the number of needed multiply-fractured wells which are needed in “tight” formations to achieve satisfactory percentage recovery from such formations. In particular, an effective fluid-drive process for formations that have and need multiple-induced fractures, that can be applied as a primary as well as secondary oil recovery method, would be especially beneficial.
In addition to oil and gas reservoirs, a similar problem occurs in tight coal-bed methane formations. Methane is adsorbed on the coal, and is recovered by de-pressuring the formation, which provides only partial release of the methane from the coal surface. What is needed is an effective fluid drive process, ideally using CO2, which adsorbs much more strongly than methane.
US 2013/0048279 as best seen from FIG. 3 thereof, teaches two parallel vertical wells, a second placed a distance from the first, wherein the mechanism to produce oil or gas from the formation is located at the second well.
US 20120168182 and US 20080087425 both teach inter alia a method for producing oil and/or gas comprising injecting a miscible enhanced oil recovery formulation into fractures of a formation for a first time period from a first well; producing oil and/or gas from the fractures, from a second well for the first time period; injecting a miscible enhanced oil recovery formulation into the fractures for a second time period from the second well; and producing oil and/or gas from the fractures from the first well for the second time period.
US 2006/0289157 teaches a process using gas-assisted gravity drainage, comprising placing one or more horizontal producer wells near the bottom of a pay zone of a subterranean hydrocarbon-bearing reservoir and injecting a fluid displacer such as CO2 through one or more vertical wells or horizontal wells. Pre-existing vertical wells may be used to inject the fluid displacer into the reservoir. As the fluid displacer is injected into the top portion of the reservoir, it forms a gas zone, which displaces oil and water downward towards the horizontal producer well(s).
US 2006/0180306 teaches a method for recovering crude oil from subterranean reservoirs by injecting both water and a second less dense fluid to displace the oil, preferably through horizontal wells.
U.S. Pat. No. 8,122,953 teaches inter alia a method of improving production of fluid from a subterranean formation including the step of propagating a generally vertical inclusion into the formation, from a generally horizontal wellbore intersecting the formation.
U.S. Pat. No. 7,441,603 teaches a method for recovery of oil from impermeable oil sands, comprising providing vertical fractures using horizontal or vertical wells. The same or other wells are used to inject heated pressurized fluids and to return the cooled fluid for reheating and recycling. The heat transferred to the oil shale gradually matures the kerogen to oil and gas as the temperature in the shale is brought up, and also promotes permeability within the shale in the form of small fractures sufficient to allow the shale to flow into the well fractures
U.S. Pat. No. 7,069,990 teaches a process for enhanced oil recovery, comprises providing at least one production well and one injection well; and injecting into the target stratum a slurry formed from sand, viscous liquids or oily sludge, which is delivered at or near formation fracture pressures. Monitoring of bottom hole pressure is carried out, to permit delivery of the slurried wastes in a series of injection episodes.
U.S. Pat. No. 4,733,726 teaches a method for recovery of oil, which provides injection of steam via an injection well into the formation and oil is recovered until there is steam breakthrough at the production well. Thereafter, the production well may be shut in or throttled while continuing injection of the steam until the bottom-hole injection pressure is greater than the vertical pressure created by the overburden thereby causing the formation to fracture horizontally. A third cycle is initiated in which oil is recovered from the formation from either the production well or the injection well or both until the amount of oil recovered is unfavorable.
U.S. Pat. No. 4,687,059 teaches injection of water into a subterranean formation followed by the injection of a polymer solution to drive oil toward a production well. The polymer solution may thermoelastically fracture the formation behind an oil-water bank to increase the injectivity rate.
U.S. Pat. No. 4,068,717 teaches a oil recovery process by injecting steam into an injection well penetrating the reservoir sufficiently to fracture the tar sand and provide passage for the steam through the tar sand to a production well piercing a tar sand reservoir.
None of the above prior art, however, teaches anything about creating, in alternating arrangement, injection fissures and producing fissures, to sweep a formation.
What is needed is a hydrocarbon recovery method for use in conjunction with multiple-fractured tight reservoirs, so as to reduce or limit the rapid decline in pressure in the formation which typically results, and to limit the number of needed multiply-fractured wells which are needed in “tight” formations to achieve satisfactory percentage recovery from such formations. In particular, an effective fluid-drive process for formations that have multiple-induced fractures, that can be applied as a primary as well as secondary oil recovery method, would be especially beneficial.